Recently, SiO2, Si3N4, Phosphor Silicon Glass (PSG), or Boron Phosphor Silicon Glass (BPSG) is used as an electric insulation thin film for a Flat Panel Display (FPD) such as Liquid-Crystal Display (LCD), etc. Further, Li2SiO3 (lithium silicate) superior in heat resistance to the above insulation films has been developed in late years. (e.g., Japanese Unexamined Patent Application Laid-Open Nos. Hei 8-45723 and 2002-265817) Furthermore, Japanese Unexamined Patent Application Laid-Open Nos. Hei 8-45723 and 2002-265817 respectively disclose a method of applying an aqueous solution of lithium silicate comprising Li2O and SiO2 over a substrate and drying as a lithium silicate film-forming method over the surface of the substrate. Moreover, WO97/20962 (PCT International Publication corresponding to Japanese PCT Patent Publication No. P2000-509100A) discloses a film-forming method employing sputtering of lithium.
A lithium silicate film-forming method by spin coating method, mist deposition method or Chemical Vapor Deposition (CVD) method is conceivable; however, it was disadvantageous being incapable of uniformly atomizing or vaporizing because the aqueous solution of the material for forming insulation film was in gel-like state. Further, merely replacing the water in the material by an organic solvent was not efficient in mixing homogeneously because solubility was small. Therefore, the lithium silicate film-forming by the above methods were not practical because they provide an insulation film of lower quality than sol-gel method or sputtering method.
Particularly when a liquid material made by dissolving solid materials in a solvent of tetrahydrofuran and so on is vaporized by CVD method after being fed to a vaporizer, the conventional method had problems not only that it hardly provides homogenuous materials but also that it easily precipitate solid materials because only solvent vaporizes with the temperature rise caused by the great difference between the vaporization temperature of the solid materials and the vaporization temperature of the solvent.
As thus described, a lithium silicate insulation film-forming by spin coating method, mist deposition method or CVD method is considered to be difficult, however, insulation film-forming by these method, particularly by CVD method makes it possible to expect providing an insulation film of high quality and high purity.